The present invention relates to the field of liquid crystal display panels, and more particularly to liquid crystal display panels having a narrow picture frame outside the display area.
A widening range of sizes, from small to large, of liquid crystal display panels is being manufactured in response to the broadening array of applications in which they are being used. In particular, liquid crystal display panels are being increasingly commercialized in an unprecedented variety of applications that exploit their advantages of being light, thin, and small. Such applications include notebook PCs with large display screens in proportion to their size (large effective screen percentage, and narrow picture frame), and liquid crystal display panels for car navigation using the maximum screen size within the provided mounting area. Studies on minimizing the width of the screen periphery (hereafter referred to as the xe2x80x98framexe2x80x99) are actively proceeding.
One configuration example of a conventional liquid crystal display panel with a narrow frame is described next with reference to drawings.
FIG. 7 shows a plan view of a part of the periphery of a general thin film transistor (TFT) active matrix color liquid crystal display panel. FIG. 8A shows a sectional elevation view taken along the line 8Axe2x80x948A in FIG. 7, and FIG. 8B shows a sectional elevation view taken along 8Bxe2x80x948B in FIG. 7.
As shown in FIGS. 7, 8A, and 8B, a typical liquid crystal display panel of the prior art includes a first and a second substrate with a liquid crystal material therebetween. The second substrate 2 is made of glass and is cut out to be smaller than the first substrate 1, also made of glass. A common electrode 8 on the second substrate 2 is connected to a connecting terminal electrode 6 provided on the first substrate 1 using conductive paste 18. Power is supplied to the common electrode from the first substrate 1. A sealing adhesive 3 is applied to the periphery of the substrates for sealing a liquid crystal layer between the first and second substrates. The path of the sealing adhesive 3 does not follow exactly the periphery of the first substrate but provides a number of indentations to allow placement of the conductive paste 18.
Glass fiber spacers 11 of several micrometers in diameter are mixed into the sealing adhesive 3 at a few weight percentages to secure the required gap between the two substrates.
For small panels, the conductive paste 18 in contact with the connecting terminal electrode 6 in FIG. 7 may be disposed only at the corners of the substrate and not the sides. For panels above 7 inches (medium size), conductive paste 18 is necessary also along the sides of the substrate to ensure uniformity of voltage within the panel.
In general, a narrower frame is achieved by making the sealing adhesive 3 strip narrower, reducing the distance between the end of the display area D and the sealing adhesive 3, or changing the position and reducing the area on which to apply the conductive paste 18.
However, it making the sealing adhesive strip 3 narrower is limited to a certain minimal width to maintain adhesion strength and moisture resistance. The distance between the end of the display area D and the sealing adhesive 3 is also limited to a certain minimal width because of limitations in application accuracy of the sealing adhesive 3 or disorder in the orientation of liquid crystal at the ends of sealing, or at the ends of an orientation film 7. Furthermore, if the position where the conductive paste 18 is applied is set too far towards the outer edge of the substrate, it may cause defect in the glass cutting step due to interference with the cut line of the second substrate 2. If the position is too far inside the edge, the conductive paste 18 mixes with the sealing adhesive 3, and may destroy the sealing. To secure an electrical connection, reduction of the area of the conductive paste 18 may also be limited to a certain minimal area.
Use of a higher purity conductive paste 18 in the liquid crystal layer 4 has also been tried. However, this measure still requires the conductive paste 18 to be applied outside the display area D, and further requires a certain distance to be maintained between the conductive paste 18 and display area D since the non-orientation region of liquid crystal occurs at the periphery of the conductive paste, resulting in little improvement in narrowing the frame.
Although there is an increasing demand for narrower frames, a minimum width of 0.8 mm is necessary due to the presence of conductive paste on the sides of the substrate.
To counteract this limitation, Japanese Laid-open Patent No. S63-29729 discloses a method for adding conductive material to the sealing adhesive, instead of the application of a separate conductive paste, to allow electrical connection between the common electrode on the second substrate and the connecting terminal electrode on the first substrate. This configuration, however, risks a short-circuit between the common electrode on the second substrate and the various other conductors on the first substrate, resulting in difficulty in narrowing the frame.
The present invention aims to offer a liquid crystal display panel with a narrow frame, even for active matrix liquid crystal display devices with many complicated wiring.
A liquid crystal display panel according to the present invention includes a first substrate having pixel electrodes, conductors for applying voltage to the pixel electrodes, and connecting terminal electrodes; a second substrate opposite said first substrate and spaced therefrom having common electrodes, and a sealing adhesive. The sealing adhesive contains conductive particles at a predetermined density, and seals the space between the first and second substrates along approximately the entire circumference for sandwiching a liquid crystal layer between the first and second substrates. The conductive particles in the sealing adhesive electrically connect the connecting terminal electrodes on the first substrate and the common electrodes on the second substrate.
The liquid crystal display panel of the present invention further includes a sealing adhesive containing spherical conductors dispersed approximately uniformly at a predetermined concentration along the periphery between the two substrates. The spherical conductors in the sealing adhesive electrically connect the common electrodes on the second substrate and the connecting terminal electrodes on the first substrate. An insulation film is provided over the conductors of the first substrate at least at the area where the conductors on the first substrate and the common electrodes on the second substrate overlap.
With the above configuration, spherical conductors in the sealing adhesive electrically connect common electrodes on the second substrate to connecting terminal electrode on the first substrate. The insulation film provided over the other conductors insulates the conductors on the first substrate from the common electrodes on the second substrate. The conventional need for connecting them using the conductive paste is eliminated. Thus, the need for allowing an area in the frame for the conductive paste is eliminated. Accordingly, a liquid crystal display panel with a narrower frame is made possible.
Furthermore, by placing the connecting terminal electrodes of the first substrate on the insulation film enables designing a larger area for the connecting terminal electrode. Since the formation of the connecting terminal electrode is the last step in fabricating the first substrate, a residue will not remain on a film surface. This assures good electrical connection, and reduces the connection resistance with the common electrodes on the second substrate.